Pressure-sensitive recording materials are generally composed of an upper sheet comprising a support having provided thereon a microcapsule layer containing microcapsules prepared by dissolving a substantially colorless color former in an appropriate solvent and encapsulating oil droplets of the solution; a lower sheet comprising a support having provided thereon a color developer layer containing an electron accepting compound (hereinafter referred to as color developer); and, if desired, an intermediate sheet comprising a support having provided on one side thereof a microcapsule layer and on the other side thereof a color developer layer.
Another type of pressure-sensitive recording material comprises a support having provided thereon a recording layer containing both the aforesaid microcapsules and a color developer.
In still another type, either the aforesaid microcapsules or the color developer may be incorporated into a support, with the other being coated thereon. The details for these pressure-sensitive recording materials are described, e.g., in U.S. Pat. Nos. 2,505,470, 2,505,489, 2,550,471, 2,730,457, and 3,418,250.
The conventional pressure-sensitive recording materials suffer from serious disadvantages in that the microcapsule layer containing a color former has insufficient light-resistance and the color developed has insufficient fastness to light. That is, the color developability of the recording material is reduced by exposure of the microcapsule layer to light, and the color density obtained with the color developer is reduced due to light exposure.
It has been proposed to use hydrated quinoline derivatives, p-phenylenediamine derivatives, and the like in an attempt to improve light-fastness of the color image formed on a pressure-sensitive recording material. However, the effectiveness in improving the light-fastness of the color image attained by these compounds proved unsatisfactory. Besides, these compunds are virtually ineffective to improve the light-resistance of the microcapsule layer.